The present invention relates to high capacity industrial casters.
Casters have long been used to move objects, including the common examples found on shopping carts and office chairs. Casters allow a user to move a cart or chair along the floor with ease. If a user wishes to move the object in a straight line, a rigid caster may be used. In applications where straight-line movement is not feasible, a swivel caster must be used. For example, a shopping cart may have a pair of rigid casters on the back and a pair of swivel casters on the front, allowing a user to steer in the cart around the isles at the supermarket.
Casters are not limited to light duty applications such as shopping carts and office chairs, but are also used in heavy-duty applications. For example, industrial strength casters can carry more than 3500 lbs., permitting a user to move heavy objects such as bulk metals, heavy equipment and the like. Because the high stresses caused by the heavy weight, the vast majority of components of past high capacity swivel casters was constructed of heavy dropped forged steel. The resulting caster was heavy, expensive (because of the amount of steel used) and corroded easily. Moreover, the heavy weight increased transportation/operation costs because it required transporting the dead weight of the heavy caster.
A need therefore exists for a heavy-duty caster that is lightweight and consequently less expensive to maintain, operate and manufacture.
An aspect of the invention involves a lightweight high capacity industrial caster. The caster includes three major parts: an upper assembly, a lower assembly, and a roller assembly. The upper assembly includes an upper plate with a first top surface and first bottom surface, the first bottom surface having a circular upper race groove within the plane of the upper plate, a kingpin having a top end and a bottom end, connected to the upper plate on the top end and extending downwardly away from the first bottom surface, the kingpin centered with respect to the circular upper race groove and an upper race insert carried in the upper race groove. The lower assembly includes a lower plate with a second top surface and a second bottom surface, the second top surface having a circular lower race groove within the plane of the lower plate, a hole in the lower plate at the center of the circular lower race groove through which the kingpin extends, a lower race insert carried in the lower race groove, a first set of bearings carried in the lower race insert. Finally, the roller assembly includes two roller support members extending downwardly away from the second bottom surface, and a roller structure attached to the two roller support members and is adapted to rotate.
Implementation of this aspect of the invention may include one or more of the following: A bearing assembly is connected to the second bottom surface, and centered about the kingpin, and includes a second set of bearings located radially about the kingpin, the kingpin extending through the bearing assembly. A fastener attaches to the bottom end of the kingpin to hold the upper assembly and lower assembly together and is adapted to allow the lower assembly to rotate about the rotational axis relative to the upper plate.
Also, the lower race insert may be free to move laterally within the plane of the lower plate, while the upper race insert is substantially immobile in the plane of the upper plate. Alternatively, the upper race insert may be free to move laterally within the plane of the upper plate, while the lower race insert is substantially immobile in the plane of the lower plate. Preferably, the first set of bearings is a plurality of ball bearings and the second set of bearings is a plurality of tapered roller bearings, both sets of bearing constructed of a heavy weight metal selected from the group consisting of steel, iron, iron alloys and steel alloys. The upper and lower race inserts, along with the kingpin, are also preferably constructed of the heavy weight metal. The upper plate, lower plate, and the two roller support members are constructed of a light metal selected from the group consisting of aluminum and aluminum alloys. The roller assembly is offset from the rotational axis. For added strength the lower plate and the two roller support members are formed as one continuous structure.
Accordingly, it is a primary object of the present invention to provide a lightweight high capacity caster that is less costly to construct, operate and maintain. This and further objects and advantages will be apparent to those skilled in the art in connection with the drawings and the detailed description of the preferred embodiments set forth below.